package class202204._26_30._26;

import java.util.Scanner;

public class demo20220426 {
    public static int func(int[] array){
        int ret = 0;
        for (int i = 0; i < array.length; i++) {
            ret ^= array[i];
        }
        return ret;
    }

    public static void main1(String[] args) {
        int[] array = {1,2,3,2,1};
        int ret = func(array);
        System.out.println(ret);
    }
    public static double sum(int n){
        Scanner scanner=new Scanner(System.in);
        float h=scanner.nextFloat();
        if (n-1 == 0){
            return h;
        }
        double sum = h + 1/2*h*sum(n-(n-1));
                return sum;
    }

    public static void main(String[] args) {
        System.out.println(sum(3));
    }
}
